water and ammonia have different molar heats of vaporization. the best interpretation at the molecular level is that water molecules

have stronger intermolecular attractions

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water has stronger inter-molecular forces.

have stronger intermolecular forces compared to ammonia molecules.

To understand this, let's first explain what molar heat of vaporization is. The molar heat of vaporization is the amount of heat energy required to vaporize one mole of a substance at its boiling point while keeping the temperature constant.

Water molecules have stronger intermolecular forces compared to ammonia molecules due to hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom in a molecule is attracted to a highly electronegative atom (such as oxygen or nitrogen) in another molecule.

In the case of water (H2O), each molecule has two hydrogen atoms bonded to an oxygen atom. The oxygen atom is highly electronegative, causing the hydrogen atoms to carry a partial positive charge. This leads to the formation of hydrogen bonds between the positive hydrogen atoms of one water molecule and the negative oxygen atoms of neighboring water molecules.

Ammonia (NH3) molecules also experience intermolecular forces, but they are weaker compared to hydrogen bonding in water. Ammonia molecules form hydrogen bonds as well, but to a lesser extent. This is because nitrogen is less electronegative than oxygen, resulting in weaker attractions between ammonia molecules compared to water molecules.

Due to the stronger intermolecular forces, water requires more energy (higher molar heat of vaporization) to break these hydrogen bonds and convert the liquid into vapor during boiling. On the other hand, ammonia with weaker intermolecular forces has a lower molar heat of vaporization, as fewer intermolecular bonds need to be overcome for vaporization to occur.

Thus, the difference in molar heat of vaporization between water and ammonia suggests that water molecules have stronger intermolecular forces arising from hydrogen bonding, while ammonia molecules have relatively weaker intermolecular forces.